Sir Keir, who led the Crown Prosecution Service (CPS) from 2008 to 2013, was not personally involved in the case, but has previously apologised on behalf of the CPS for its failures.
Critics, including numerous Conservative MPs, have decried Johnson's claim - made during a fractious parliamentary session - noting it has been propagated by far-right conspiracy theorists.
Johnson later clarified the remark, saying he accepted Sir Keir played no direct role in the decision, but noting his apology and apparent acceptance of responsibility.
The prime minister has refused to apologise or to retract his accusation.
However, it has come under fresh scrutiny after several dozen anti-lockdown demonstrators mobbed Sir Keir outside parliament on Monday (7), with one protester heard claiming he was "protecting paedophiles".
British Labour Party leader Keir Starmer gets into a police car as protesters surround him shouting slogans in London, Britain February 7, 2022, in this still image obtained from a social media video on February 8, 2022. (Courtesy of Conor Noon/via REUTERS)
A video posted online showed the Labour leader being jostled before police, who arrested two people, intervened and escorted him to a car.
Within hours, Tory and other lawmakers were repeating calls for Johnson to say sorry.
"PM - apologise please," Conservative MP Tobias Ellwood wrote on Twitter.
"Let's stop this drift towards a Trumpian style of politics from becoming the norm. We are better than this."
Ellwood is one of 13 Tory MPs to have publicly submitted a no-confidence letter in Johnson to a committee of backbench lawmakers with the power to call a leadership contest.
Green Party MP Caroline Lucas said on Tuesday that Johnson's attack was "utterly shameful" and "straight out of (the) Trumpian playbook".
"Words have consequences - we saw that on (the) streets of Westminster yesterday evening. He's poisoning our politics & must apologise or go."
Johnson himself took to Twitter to criticise Sir Keir’s treatment on Monday as "absolutely disgraceful".
"All forms of harassment of our elected representatives are completely unacceptable," he said, adding: "I thank the police for responding swiftly."
His spokesman told reporters Johnson would not be apologising to Sir Keir, and insisted he "always seeks to engage with people in the right way".
However, House of Commons Speaker Lindsay Hoyle warned MPs their "words have consequences" and reiterated that Johnson's original claim was "inappropriate" and could "inflame opinions".
But the incidents appear to have heightened unease within the Conservative Party at Johnson's conduct - just as he attempts a major reset after months of tumult.
More MPs are thought to have sent letters in without declaring them, sparked mostly by damaging allegations of parties in Downing Street during the pandemic in a scandal dubbed "partygate".
The committee requires at least 15 per cent, or 54, of the 360 Conservative MPs to write such letters to trigger a party leadership challenge.
Meanwhile, Johnson is awaiting the outcome of a Metropolitan Police Service investigation into the numerous Downing Street gatherings and whether lockdown rules were breached.
The under-fire British leader could face the humiliation of being fined by police - an outcome likely to prompt a flurry of further no-confidence letters.
He is also heading into UK local elections in May with Labour enjoying a double-digit lead over his ruling Tories, on the back of "partygate" and a squeeze on living standards caused by surging inflation.
PRIME MINISTER Keir Starmer will travel to Egypt to attend the Sharm El Sheikh Peace Summit, where leaders are expected to sign a US-brokered peace agreement aimed at ending the conflict in Gaza, his office said.
The first phase of the plan is set to begin with the release of hostages and Palestinian prisoners by Monday (13), marking what Britain called a "historic turning point" after two years of war.
He is expected to call for continued international coordination to implement the next phase, which includes deploying a ceasefire monitoring mission and establishing transitional governance in Gaza.
Starmer will reiterate Britain's "steadfast support" to help secure the ceasefire and deliver humanitarian aid.
Trump and his Egyptian counterpart Abdel Fattah al-Sisi will chair the summit, also attended by world leaders including the UN chief.
The gathering in the Red Sea resort town will bring together "leaders from more than 20 countries", Sisi's office said.
UN Secretary-General Antonio Guterres said he will attend, as will Italian prime minister Giorgia Meloni and Pedro Sanchez of Spain.
French president Emmanuel Macron and Turkish president Recep Tayyip Erdogan will also travel to Sharm el-Sheikh, according to their offices.
The European Council will be represented by its president, Antonio Costa, a spokesperson said.
"The plan offers a real chance to build a just and sustainable peace, and the EU is fully committed to supporting these efforts and contributing to its implementation," the spokesperson added.
Jordan's King Abdullah II is also expected to attend, according to state media.
There was no immediate word on whether Israeli prime minister Benjamin Netanyahu would participate, while Hamas has said it will not take part.
Hossam Badran, a Hamas political bureau member, said that the Palestinian militant group "will not be involved".
Hamas "acted principally through... Qatari and Egyptian mediators" during previous talks on Gaza, he said.
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